During the 17th-Century, the plague hit London very badly with almost a 1/3 of the population being killed by the disease. Now, this is pretty macabre but lots of the small parks and green spaces actually became vast plague pits where tens of thousands of bodies were left.
Some of the most famous are in; Golden Square Park in Soho, Green Park, Knightsbridge Green, and at the start of the Bakerloo Line in Elephant and Castle.
Thankfully, it’s definitely one of the more hidden London places and facts that isn’t in plain sight anymore. Try not to think of that next time you’re in the park, though!